Joseph Daniel

Metal-on-metal resurfacing of the hip in patients under the age of 55 years with osteoarthritis

The results of conventional hip replacement in young patients with osteoarthritis have not been encouraging even with improvements in the techniques of fixation and in the bearing surfaces. Modern metal-on-metal hip resurfacing was introduced as a less invasive method of joint reconstruction for this particular group. This is a series of 446 hip resurfacings (384 patients) performed by one of the authors (DJWM) using cemented femoral components and hydroxyapatite-coated uncemented acetabular components with a maximum follow-up of 8.2 years (mean 3.3). Their survival rate, Oxford hip scores and activity levels are reviewed. Six patients died due to unrelated causes. There was one revision (0.02%) out of 440 hips. The mean Oxford score of the surviving 439 hips is 13.5. None of the patients were told to change their activities at work or leisure; 31% of the men with unilateral resurfacings and 28% with bilateral resurfacings were involved in jobs that they considered heavy or moderately heavy; 92% of men with unilateral hip resurfacings and 87% of the whole group participate in leisure-time sporting activity. The extremely low rate of failure in spite of the resumption of high level occupational and leisure activities provides early evidence of the suitability of this procedure for young and active patients with arthritis.

Pseudotumors associated with total hip arthroplasty.

Pseudotumors are a rare but important complication occurring with all types of hip replacements.The true prevalence of pseudotumors is debated.Potential causes of pseudotumors may include foreign-body reaction, hypersensitivity, and wear debris.The conduct of clinical trials on the incidence, causes, and treatments of pseudotumors has been inadequate as few investigators have used a randomized controlled design to compare various implant types.

Mini-incision resurfacing arthroplasty of hip through the posterior approach.

The success of metal-on-metal hip resurfacing in the medium term in young and active patients is becoming evident. The procedure now can be done using a minimal approach developed by the senior author using a single posterior incision. This mini-incision resurfacing arthroplasty of the hip has made resurfacing more attractive to surgeons and patients. But does a mini incision approach allow reliable component placement? The results of 232 consecutive Birmingham Hip Resurfacings done using this approach between January and December 2004 are presented. Mean incision length was 11.8 cm. Seventy-seven percent of the incisions were between 9 and 12 cm long. Body mass index of the patients studied ranged from 17.6 to 46.7. Comparing the traditional approach with the mini-incision resurfacing arthroplasty of hip did not show a difference between the two groups in terms of operating time. The mean hospital stay was reduced by a day in the mini-incision group. The mean inclination of the acetabular components was within the target range in the two groups. Patient feedback shows that reduced postoperative pain, faster recovery rate, and better cosmesis make the mini-incision approach very popular. Although the mini incision is indeed appealing, it has a steep learning curve. In the early phase of the learning curve, care should be taken to avoid suboptimal component placement, which has the potential to affect long-term outcome adversely. Level of Evidence: Therapeutic study, Level III (retrospective comparative study). See the Guidelines for Authors for a complete description of levels of evidence.

Renal Clearance of Cobalt in Relation to the Use of Metal-on-metal Bearings in Hip Arthroplasty

BACKGROUND A concern regarding the use of metal-on-metal bearings in hip arthroplasty has been that the high levels of metal ions that are released overwhelm the renal threshold for metal excretion, leading to systemic buildup of metals. The purpose of this investigation was to determine if the physiological renal capacity for cobalt clearance and cobalt concentrating efficiency is overwhelmed by the elevation in metal ion levels seen in patients with metal-on-metal-bearing hip devices. METHODS Concurrent specimens of urine and plasma were obtained from a group of 461 patients (346 men and 115 women) at various intervals after either a unilateral (296) or a bilateral (130) metal-on-metal hip arthroplasty or preoperatively (thirty-five patients; the control specimens). Metal ion analyses were performed with high-resolution inductively coupled mass spectrometry. Renal efficiency was measured as the ratio of urine cobalt concentration to plasma cobalt concentration. Cobalt clearance was calculated by dividing the urine cobalt output in twenty-four hours by the plasma cobalt concentration. Dividing the quotient by 1440 adjusts it to clearance per minute. RESULTS The median renal efficiency was found to be 0.9 in the analysis of the preoperative specimens, indicating that there was renal conservation of cobalt. In patients with metal-on-metal bearings, the median renal efficiency was 3.2, indicating that, as a result of cobalt excretion, the cobalt concentration in urine was threefold higher than the concentration in plasma. Linear regression analysis showed that renal efficiency progressively increased at a rate of 9% for every microg/24 hr increase in cobalt release. Cobalt clearance showed a similar trend, increasing from 1.3 mL/min in the preoperative group to 3.7 mL/min in the follow-up group. In the follow-up group, renal cobalt clearance progressively increased from 1.9 to 7.1 mL/min with increasing daily cobalt output, which indicates that with increasing in vivo metal ion release there was a progressive increase in the rate at which the kidneys cleared the plasma of cobalt. CONCLUSIONS In subjects with no prosthetic device, the kidneys tend to conserve cobalt in the body. We found that, in patients with a metal-on-metal hip prosthesis, there is a progressive increase in cobalt clearance with increasing in vivo wear at the levels of cobalt release expected in patients with an array of metal-on-metal-bearing total joint arthroplasties. We found no threshold beyond which renal capacity to excrete these ions is overwhelmed.

A five-year radiostereometric follow-up of the Birmingham Hip Resurfacing arthroplasty.

The early designs of hip resurfacing implants suffered high rates of early failure, making it impossible to obtain valuable mid-term radiostereophotogrammetric (RSA) results. The metal-on-metal Birmingham Hip Resurfacing arthroplasty has shown promising mid-term results and we present here the first mid-term RSA analysis of a hip resurfacing implant. The analysis was performed in 19 hips at five years post-operatively. The mean acetabular component translation and rotation, and femoral component translation were compared with the previous RSA measurements at two and six months, and one and two years. There was no statistical significance (t-test, p < or = 0.05) between these consecutive movements, indicating the mid-term stability of the implant.

Failure of a Novel Ceramic-on-Ceramic Hip Resurfacing Prosthesis

We report the early failure of five ceramic-on-ceramic hip resurfacings (CoCHRs). The ceramic used for the acetabular liner was a novel ceramic-composite (two thirds polyurethane and one third alumina ceramic). All cases were revised for increasing metal ion levels (blood cobalt 3.93-208.0 μg/l and chromium 1.57-17.5 μg/l) due to ceramic liner fracture and/or accelerated wear of the ceramic femoral head coating. Patients underwent bearing exchange and revision using primary hip arthroplasty implants at a mean of 3.0 years following CoCHR. Intraoperatively all patients had metallosis. At 1 to 2 years of follow-up blood metal ions normalized with no complications. We do not recommend this particular type of ceramic-on-ceramic bearing for hip resurfacing.

Patient Selection and Timing of Operation

Hip resurfacing arthroplasty is an option for people with advanced hip disease who would otherwise receive and are likely to outlive a conventional primary total hip replacement (THR), particularly for younger patients who wish to be reasonably active [1]. That guideline from the National Institute for Clinical Excellence (NICE), a statutory body in the United Kingdom, broadly sums up the indications in which a hip resurfacing device should be used.

Management of Complex Anatomy

Traditionally, there have been attempts to classify hip instability into two distinct entities (i.e., congenital and developmental). This distinction is rather poorly defined, and instability of the hip due to acetabular insufficiency presents as a broad spectrum of conditions with varying severity. Crowe et al. [1] classify dysplastic hips into four grades on the basis of proximal displacement of the femoral head. In grade I, the femoral head is displaced by a distance that is equivalent to 50% of its diameter. In grades II, III, and I V, the displacement is 50% to 75%, 75% to 100%, and greater than 100% of the femoral head, respectively. Hartofilakidis et al. [2] classify dysplasia into three types: (a) dysplasia, in which the socket is shallow but the femoral head is contained within the original true acetabulum, (b) low dislocation, in which the femoral head articulates with a false acetabulum, which is distinct from the true acetabulum but overlaps it, and (c) high dislocation, in which there is no contact between the true and the false acetabulum.

A two-year radiostereometric follow-up of the first generation Birmingham Mid Head Resection arthroplasty

During the first decade of the 21st century, metal-on-metal hip resurfacing became one of the main treatment options for younger, more active patients with osteoarthritis. However, as a result of the reported failure rate of both total hip replacement (THR) and resurfacing in patients with considerable loss of bone stock in the femoral head (e.g. in extensive avascular necrosis), other solutions have been sought for these patients. The short-stemmed Birmingham Mid Head Resection prosthesis (BMHR) combines a metal-on-metal articulation and a femoral neck preserving feature. In this study, radiostereometric analysis (RSA) was used to study migration of the BMHR femoral component in 13 hips. Translations and rotations were measured up to two years. Relative values showed no statistically significant migration. Absolute values demonstrated settling in occurring between zero and two months postoperatively in all directions studied. From two months to two years no significant migration occurred except for rotation around the x-axis of the femoral segment (p = 0.049). After initial settling-in, absolute values were low, indicating that there was no evidence of early migration or loosening of the components.

Results of Birmingham Hip Resurfacing in Different Diagnoses

The results of total hip arthroplasty in young patients have been uniformly worse than those in older patients. In a recent series [1], the Swedish Hip Arthroplasty Register reports 10-year survival rates of 65.8%, 66.6%, and 64.0% with cemented, uncemented, and hybrid implants, respectively, in male patients under the age of 55 years with osteoarthritis (OA). This led them to the conclusion that this young cohort is epidemiologically and demographically different from older patients with OA and that there is an obvious need to increase the usage of alternative and conservative methods in the treatment of these patients. It is this high incidence of early failures of conventional total hip arthroplasties that drove the search for a more conservative solution and led to the resurgence of modern resurfacing.